The following invention relates to fixtures for checking effective tooth spacing along the pitch circle diameter of a splined or gear-like member having exterior or interior teeth.
As with all mass produced products, gears and other toothed parts must be checked to determine whether the production process has produced the results that were desired. Such inspection is somewhat difficult in the case of gears because of their irregular shape and the number of factors that must be checked. Among the factors that must be checked is the accuracy of tooth dimensions; such as, lead, profile thickness, spacing, and depth. Tooth spacing must be uniform and correct within very strict tolerances. As an example, a splined clutch plate for use in an automatic transmission must have a tolerance of 0.002 at a pitch diameter of approximately six inches on a clutch plate which is approximately 0.050 inches thick. To insure correct tolerances, a checking device must be used that is extremely accurate.
A common way for checking the thickness of gear-teeth along the pitch circle diameter is by using a gear-teeth vernier caliper. A vernier caliper generally has two members which are connected in a generally "F" shaped formation with one of the members being moveable with respect to the other. To check the tooth thickness at the pitch circle the members are adjusted until they both contact the sides of the gear tooth; then the distance between the two members can be measured and the thickness of the tooth determined.
A problem with this type of gear checking device is the inability to check the effective tooth spacing which takes into consideration the cumulative error in size and spacing of all teeth at the pitch circle diameter.
In U.S. Pat. No. 2,561,533 issued to J. J. Parker on July 24, 1951, adjustable tooth gauges are disclosed which permit teeth on diametrically opposite sides to be checked. The adjustable tooth gauges of Parker are used to check gears having internal teeth or external teeth. Both types of gauges are similarly constructed, having two complementary ring-like body portions disposed in face to face relationship and angularly adjustable relative to each other about their common central axis. Each body member is provided with a complementary portion of each gauging tooth around the full pitch circle. When the body portions are rotatably indexed relative to each other, the paired segments of each tooth are moved toward or away from each other along the pitch circle to determine the overall effective width of a master gauging tooth, or gauging tooth of known size. A disadvantage of the Parker adjustable tooth gauge is that it did not provide any data on the effective size of each individual part checked. Parker's concept required setting the gage to a pre-determined tooth thickness and then using it as a functional "go" or "no go" check. Due to the accuracy required in checking gears and splines, if the partial teeth are worn or damaged in any way a false gauging will be obtained, rendering the gauge inaccurate.
Another prior art device was an actuating spline gage wherein each tooth portion of the gage comprised three axially stacked segments, the outer two being stationary (to stabilize the unit against misalignment) and the central one being indexable. With such three-piece construction, all three portions of each tooth had to contact the tooth of the part being inspected, thereby placing a practical limit on the thinness of the parts which could be inspected.